Systems and methods for improved detector assembly sizing

ABSTRACT

A detector assembly is provided that includes a semiconductor detector, a collimator, and a processing unit. The semiconductor detector has a first surface and a second surface opposed to each other. The first surface includes pixelated anodes, and the second surface includes a cathode electrode. The collimator includes openings defined by septa. The collimator defines a pitch D between adjacent septa, with the septa defining a septa length L. A ratio of L/D is less than 14. The processing unit is configured to identify detected events within virtual sub-pixels distributed along a length and width of the semiconductor detector. Each pixel comprises a plurality of corresponding virtual sub-pixels, and absorbed photons are counted as events in a corresponding virtual sub-pixel.

BACKGROUND OF THE INVENTION

This application is a continuation application of, and claims benefit tothe filing date of, U.S. patent application Ser. No. 16/001683, filed 6Jun. 2018, entitled “Systems and Methods for Improved Detector AssemblySizing,” the entire disclosure of which is incorporated by referenceherein.

The subject matter disclosed herein relates generally to apparatus andmethods for diagnostic medical imaging, such as Nuclear Medicine (NM)imaging.

In NM imaging, systems with multiple detectors or detector heads may beused to image a subject, such as to scan a region of interest. Forexample, the detectors may be positioned adjacent the subject to acquireNM data, which is used to generate a three-dimensional (3D) image of thesubject. System performance may be limited or affected by the size ofdetector units, which may impact how closely detectors may be placed toan object to be imaged, for example.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a detector assembly is provided that includes asemiconductor detector, a collimator, and a processing unit. Thesemiconductor detector has a first surface and a second surface opposedto each other. The first surface includes pixelated anodes, and thesecond surface includes a cathode electrode. The collimator includesopenings defined by septa. The collimator defines a pitch D betweenadjacent septa, with the septa defining a septa length L. A ratio of L/Dis less than 14. The processing unit is configured to identify detectedevents within virtual sub-pixels distributed along a length and width ofthe semiconductor detector. Each pixel comprises a plurality ofcorresponding virtual sub-pixels, and absorbed photons are counted asevents in a corresponding virtual sub-pixel.

In another embodiment, a detector assembly is provided that includes asemiconductor detector, a collimator and a processing unit. Thesemiconductor detector has a first surface and a second surface opposedto each other. The first surface includes pixelated anodes, and thesecond surface includes a cathode electrode. The collimator includesopenings defined by septa. The collimator defines a pitch D betweenadjacent septa, and the septa define a septa length L. The processingunit is configured to identify detected events within virtual sub-pixelsdistributed along a length and width of the semiconductor detector,wherein each pixel comprises a plurality of corresponding virtualsub-pixels, wherein absorbed photons are counted as events in acorresponding virtual sub-pixel. The virtual sub-pixels define asub-pixel pitch d, wherein a ratio of L/d is 25 or more.

In another embodiment, a method (e.g., a method of providing a detectorassembly) includes providing a semiconductor detector having a firstsurface and a second surface opposed to each other, with the firstsurface including pixelated anodes, and the second surface including acathode electrode. Further, the method includes disposing a collimatorproximate the semiconductor detector. The collimator includes openingsdefined by septa. The collimator defines a pitch D between adjacentsepta, with the septa defining a septa length L. A ratio of L/D is lessthan 14. The method also includes coupling a processing unit to thesemiconductor detector. The processing unit is configured to identifydetected events within virtual sub-pixels distributed along a length andwidth of the semiconductor detector, wherein each pixel comprises aplurality of corresponding virtual sub-pixels, wherein absorbed photonsare counted as events in a corresponding virtual sub-pixel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic block view of a detector assembly inaccordance with various embodiments.

FIG. 2 provides assembly schematic plan view of a semiconductor detectorof the detector assembly of FIG. 1.

FIG. 3 provides a schematic plan view of a collimator of the detectorassemlby of FIG. 1.

FIG. 4 illustrates an exploded sectional side view of a detectorassemlby in accordance with various embodiments.

FIG. 5 illustrates a schematic plan view of a semiconductor detector inaccordance with various embodiments.

FIG. 6 provides a flowchart of a method in accordance with variousembodiments.

FIG. 7 provides a flowchart of a method in accordance with variousvarious embodiments.

FIG. 8 illustrates various combinations of sub-pixel pitch and septaheight.

FIG. 9 illustrates a schematic plan view of a collimator with septa thatare not aligned with boundaries of corresponding pixelated anodes inaccordance with various embodiments.

FIG. 10 is a schematic block diagram of a Nuclear Medicine (NM) imagingsystem in accordance with various embodiments.

FIG. 11 is a schematic block diagram of a Nuclear Medicine (NM) imagingsystem in accordance with various embodiments.

FIG. 12 illustrates detector head sizes for various arrangements.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of certain embodiments will be betterunderstood when read in conjunction with the appended drawings. To theextent that the figures illustrate diagrams of the functional blocks ofvarious embodiments, the functional blocks are not necessarilyindicative of the division between hardware circuitry. For example, oneor more of the functional blocks (e.g., processors or memories) may beimplemented in a single piece of hardware (e.g., a general purposesignal processor or a block of random access memory, hard disk, or thelike) or multiple pieces of hardware. Similarly, the programs may bestand alone programs, may be incorporated as subroutines in an operatingsystem, may be functions in an installed software package, and the like.It should be understood that the various embodiments are not limited tothe arrangements and instrumentality shown in the drawings.

As used herein, the terms “system,” “unit,” or “module” may include ahardware and/or software system that operates to perform one or morefunctions. For example, a module, unit, or system may include a computerprocessor, controller, or other logic-based device that performsoperations based on instructions stored on a tangible and non-transitorycomputer readable storage medium, such as a computer memory.Alternatively, a module, unit, or system may include a hard-wired devicethat performs operations based on hard-wired logic of the device.Various modules or units shown in the attached figures may represent thehardware that operates based on software or hardwired instructions, thesoftware that directs hardware to perform the operations, or acombination thereof.

“Systems,” “units,” or “modules” may include or represent hardware andassociated instructions (e.g., software stored on a tangible andnon-transitory computer readable storage medium, such as a computer harddrive, ROM, RAM, or the like) that perform one or more operationsdescribed herein. The hardware may include electronic circuits thatinclude and/or are connected to one or more logic-based devices, such asmicroprocessors, processors, controllers, or the like. These devices maybe off-the-shelf devices that are appropriately programmed or instructedto perform operations described herein from the instructions describedabove. Additionally or alternatively, one or more of these devices maybe hard-wired with logic circuits to perform these operations.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralof said elements or steps, unless such exclusion is explicitly stated.Furthermore, references to “one embodiment” of are not intended to beinterpreted as excluding the existence of additional embodiments thatalso incorporate the recited features. Moreover, unless explicitlystated to the contrary, embodiments “comprising” or “having” an elementor a plurality of elements having a particular property may includeadditional elements not having that property.

Various embodiments provide systems and methods for improving imagequality. For example, various embodiments may improve one or more ofsensitivity, resolution, contrast, and distance to object being imaged.Various embodiments utilize virtual sub-pixel based sensing, forexample, to reduce energy tails.

It may be noted that sensitivity and contrast may be improved byreducing an energy tail (e.g., energy tail for a CZT detector), ortransferring events from the tail into the energy window used to countevents. One way to accomplish such a transfer is to reduce the size ofpixels or contacts. Another way is to increase the thickness of the CZTdetector. It may be noted that the thickness in practice is limited byvoltage breakdown. Further, reducing pixel size may have certaindrawbacks. For example, reducing pixel size prevents or inhibits the useof double pitch collimators due to manufacturing complexity of therequired septa sizes, and impacts sensitivity. Use of a single pitchcollimator may in turn tend to make collimator septa higher, increasingthe column diameter (or other measure of detector unit size), andnegatively impact resolution. Various embodiments address these issuesby using sub-pixel sensing in conjunction with reduced collimator septaheight, reducing detector unit size and improving detector distance topatient.

A technical effect provided by various embodiments includes improvedimage quality, for example by increasing one or more of sensitivity,resolution, or contrast of a detector system, such as a NM imagingdetector system. A technical effect provided by various embodimentsincludes reduced detector unit size, allowing for closer placement to anobject being imaged.

FIG. 1 provides a schematic block view of a detector assembly 100 inaccordance with various embodiments, and FIG. 2 illustrates a plan viewof the second surface 114 of the semiconductor detector 110. As seen inFIG. 1, the detector assembly includes a semiconductor detector 110, acollimator 120, and a processing unit 130. Generally, the semiconductordetector 110 produces signals in response to absorption events (e.g.,photons produced in response to a radiopharmaceutical that has beenadministered to an object being imaged that impact the semiconductordetector 110). The signals are provided to the processing unit 130,which uses identified events to reconstruct an image of the object beingimaged and to derive the location of the event inside the physical pixelas described, for example in U.S. patent application Ser. No. 15/280640.The collimator 120 guides photons to the semiconductor detector 110, andlimits the angular range of approach of photons to a given pixel orportion of the semiconductor detector 110, helping to allow for accuratedetermination of the portion of the object being imaged from which agiven detected event originated.

As depicted in FIGS. 1 and 2, the semiconductor detector 110 has a firstsurface 112 and a second surface 114. The second surface 114 is opposedto the first surface 112 (and, likewise, the first surface 112 isopposed to the second surface 114). The semiconductor detector 110 isconfigured to generate electrical signals in response to photon impacts.The semiconductor detector 110, for example, may be made of Cadmium ZincTelluride (CZT). The second surface 114 includes pixelated anodes 116disposed thereon, and the first surface 112 includes a cathode electrode118 disposed thereon. It may be noted that, in some embodiments, thecathode electrode 118 may be a monolithic, or single, cathode, while inother embodiments multiple cathode electrodes may be employed. Thecathode electrode 118 collects an opposite electrical charge of thepixelated anodes 116, and the pixelated anodes 116 are used to generatesignals in response to charges generated by the semiconductor detector110 responsive to photon impacts.

In various embodiments, the pixelated anodes 116 are arranged in a grid,with the location of one or more pixelated anodes 116 at which a signalis generated responsive to a photon impact used to determine acorresponding location in the object corresponding to the photon impact.Each pixelated anode 116 may also be understood as corresponding to apixel 115 of the semiconductor detector 110 or a pixel represented in animaging dataset acquired via the semiconductor detector 110. As seen inFIG. 2, the pixelated anodes 116 are arranged in a grid 200 having alength 202 and a width 204. In the illustrated embodiment, the pixelatedanodes 116 are square shaped, and have a uniform pixel pitch 210 alongboth the length 202 and width 204, or uniform spacing between adjacentpixels. It may be noted that other arrangements (e.g., different pitchesalong the length and width, varying pitch along the length and/or width,different pixel shapes) may be utilized in various embodiments.

As seen in FIG. 1, the collimator 120 is interposed between thesemiconductor detector 110 and an object 102 being imaged. Thecollimator 120 is used to control passage of radiation from the object102 being imaged to the semiconductor detector 110. The collimator 120includes openings that are configured to guide photons to thesemiconductor detector 110, limiting an angular range of approach forphotons that impact the semiconductor detector 110.

FIG. 3 illustrates a plan view of the collimator 120. As seen in FIG. 3,the depicted example includes an array 300 of openings 302 that aredefined between septa 304. The array 300 extends along a length 310 anda width 320 of the collimator 120, with the openings 302 of the depictedembodiment spaced at uniform pitch 306 along both the length 310 andwidth 320 in the illustrated example. It may be noted that, in otherembodiments, the pitch along the length 310 may differ from the pitchalong the width 320, and/or the pitch may vary along the length 310and/or the width 320. In the illustrated embodiment, each opening 302 ofthe collimator 120 is associated with a single corresponding pixelatedanode 116 (or corresponding pixel) of the semiconductor detector 110.(It may be noted that in other embodiments, as discussed herein,collimator openings may be shifted relative to pixels.) Accordingly, thearray 300 of openings 302 of the collimator 120 may be understood ashaving a 1:1 correspondence with the grid 200 of pixelated anodes 116(or corresponding pixels) of the semiconductor detector 110. The array300 of openings 302 in the illustrated embodiment corresponds to thegrid 200 of pixelated anodes 116, with radiation passing through a givenopening 302 guided to the corresponding pixelated anode 116. As such,radiation that passes through a given opening 302 is confined within asingle cell of the collimator 120, and is absorbed at a locationcorresponding to one and only one pixelated anode 116 that is associatedwith the given opening 302 (e.g., located directly beneath the opening302). FIG. 4 illustrates an exploded cross-section of the collimator 120and semiconductor detector 110 showing the septa length 308, collimatorpitch 306, and sub-pixel pitch 212 (see also FIG. 2). As seen in FIGS. 1and 4, the septa 304 define a septa length 308 and septa thickness 309.Both the septa length 308 and the pitch 306 are shown as uniform inFIGS. 1 and 3; however, it may be noted that either parameter value mayvary in various embodiments. Further, it may be noted that the depictedsepta 304 are parallel to each other, normal to the second surface 114,and define square-shaped cross sections for each collimator cell;however, it may be noted that different configurations may be employedin alternate embodiments. It may also be noted that, for the exampledepicted in FIG. 3, the collimator may be understood as a registeredcollimator, or a collimator having a collimator septa over each boundarybetween adjacent physical pixels. (It may also be noted that adual-pitch collimator may also be registered).

In some embodiments, however, the collimator may not be registered. Forexample, in some embodiment, the septa of a collimator may be shiftedrelative to pixelated anodes, with the septa not aligned with boundariesbetween the pixelated anodes. FIG. 9 illustrates a collimator 900 withsepta 902 (shown in solid lines) that are not aligned with boundaries912 (shown in dashed lines) of corresponding pixelated anodes 910. Inthe embodiment depicted in FIG. 9, the septa 902 of the collimator 900are shifted by a half pixel in both x and y directions with respect tothe boundaries 912. Accordingly, the septa 902 pass along centerlines ofthe pixelated andoes 912, and the septa 902 cross the pixel area at thecenter of the pixel, which is the pixel area with the lowest subpixelaccuracy because it is the portion of the pixel farthest away fromneighboring pixels. Accordingly, by shifting the collimator positionwith respect to pixelated anodes, the portions of the pixels with thelowest subpixel accuracy may be aligned with the septa 902.

The processing unit 130 is operably coupled to the semiconductordetector 110, and is configured to identify detected events. Thedepicted processing unit is configured to derive the location of eventswithin physical pixelated anodes 116 and, based on their location,assign them to virtual sub-pixels 117 distributed along the length 202and width 204 of the semiconductor detector 110 to be counted at theassigned location. As seen in FIG. 2, the virtual sub-pixels 117 arerepresented by dashed lines passing through the semiconductor detector110 corresponding to the location of the virtual sub-pixels 117. Thevirtual sub-pixels 117 in the illustrated example are spaced at asub-pixel pitch 212, which is half the pixel pitch 210. It may be notedthat in the illustrated examples, the semiconductor detector 110includes 2 virtual sub-pixels 117 across a width of each pixelated anode116 (or corresponding pixel), and 2 virtual sub-pixels 117 across alength of each pixelated anode 116. Each pixelated anode 116 orcorresponding pixel includes a plurality of corresponding virtualsub-pixels, with absorbed photons in the semiconductor detector 110counted as events in a corresponding virtual sub-pixel. Additionaldiscussion regarding virtual sub-pixels and the use of virtualsub-pixels, and the use of collected and non-collected charge signalsmay be found in U.S. patent application Ser. No. 14/724,022, entitled“Systems and Method for Charge-Sharing Identifcation and CorrectionUsing a Single Pixel,” filed 28 May 2015 (“the 022 Application); U.S.patent application Ser. No. 15/280,640, entitled “Systems and Methodsfor Sub-Pixel Location Determination,” filed 29 Sep. 2016 (“the 640Application”); and U.S. patent application Ser. No. 14/627,436, entitled“Systems and Methods for Improving Energy Resolution by Sub-Pixel EnergyCalibration,” filed 20 Feb. 2015 (“the 436 Application). The subjectmatter of each of the 022 Application, the 640 Application, and the 436Application are incorporated by reference in its entirety.

In various embodiments the processing unit 130 includes processingcircuitry configured to perform one or more tasks, functions, or stepsdiscussed herein. It may be noted that “processing unit” as used hereinis not intended to necessarily be limited to a single processor orcomputer. For example, the processing unit 130 may include multipleprocessors, ASIC's, FPGA's, and/or computers, which may be integrated ina common housing or unit, or which may distributed among various unitsor housings. It may be noted that operations performed by the processingunit 130 (e.g., operations corresponding to process flows or methodsdiscussed herein, or aspects thereof) may be sufficiently complex thatthe operations may not be performed by a human being within a reasonabletime period. For example, the determination of values of collected,non-collected, and/or combined charge signals within the timeconstraints associated with such signals may rely on or utilizecomputations that may not be completed by a person within a reasonabletime period.

As discussed, herein, signals are generated by one or more pixelatedanodes 116 in response to a photon impact, with the location of thepixelated anode(s) 116 generating a signal used to determine acorresponding location in the object for which an event is counted. Invarious embodiments, as also discussed in the 022 Application, the 640Application, and the 436 Application, signals from adjacent pixels maybe used to assign a virtual sub-pixel location within a given pixelatedanode 116. In some embodiments, the processing unit 130 is configured todetermine an absorption location for a given absorbed phon based onnon-collected signals received from pixelated anodes adjancent to apixelated anode abosrobing the given absorbed photon.

As discussed above, the collimator 120 has openings 302 defined betweensepta 304, with the openings 302 spaced at a pitch 306, and the septahaving length 308. The ratio of the septa length 308 to collimator pitch306 may be represented as L/D, where L is the septa length 308, and D isthe collimator pitch 306. Various embodiments provide L/D ratios, orranges of L/D ratios, that, combined with the use of virtual sub-pixelsprovide improved imaging relative to ratios of conventional detector andcollimator arrangements.

For example, various embodiments utilize a ratio of L/D (or range ofratios of L/D) of less than 14, in contrast to conventional designs thatmay use a ratio of L/D of about 20. In some embodiments, the ratio ofL/D (or range of ratios of L/D) is between 8 or more and 12 or less. Forexample, in some embodiments, a septa length of 15 millimeters andcollimator pitch of 1.5 millimeters may be employed. As another example,a septa length of 16 millimeters and collimator pitch of 1.42millimeters may be employed. By utilizing such ranges of L/D ratio inconjunction with the use of virtual sub-pixels, various technicalimprovements or effects are achieved. For example, resolution andsensitivity may be maintained (or even increased) while decreasingcollimator height. Similarly, resolution and/or sensitivity may beincreased while maintaining collimator height. Use of a smallercollimator height enables use of a detector unit or head with a smallerouter dimension (e.g., radius). Such reduced detector unit size providesthe ability to position a detector unit closer to the surface of anobject being imaged, allowing groups of detector units to more closelyapproach an object being imaged before contacting adjacent detectorunits, and/or reduces the size and/or number of gaps between detectorunits.

Various embodiments additionally or alternatively utilize novel rangesof L/d, where L is the septa length 308 and d is the sub-pixel pitch212. For purposes of comparison with designs that do not utilize virtualsub-pixels, the pitch d may be understood as being based on the smallestunit of pixel as determined by the processing unit 130. Accordingly, ifvirtual sub-pixels are not employed, the pitch d is the pixel pitch(e.g., pitch 210), but if virtual sub-pixels are employed, then thepitch d, then sub-pixel pitch (e.g., pitch 212). Various embodimentsutilize a ratio of L/d of 25 or more, in contrast to conventionaldesigns that may use a ratio of L/d of between about 8 and 20. Forexample, in some embodiments, the ratio of L/d is between 25 or more and80 or less. By way of example, in some embodiments, a septa length of 16millimeters may be used in connection with sub-pixel pitches of 0.5millimeters, 0.4 millimeters, and/or 0.2 millimeters. By utilizing suchranges of L/d ratio in conjunction with the use of virtual sub-pixels(as well as L/D ratios as discussed above in various embodiments),resolution and sensitivity may be maintained while decreasing collimatorheight.

It may be noted that while the collimator and sub-pixel pitches of theillustrated example are the same in both x and y directions (or alongthe length and width of the collimator and/or semiconductor detector),in other embodiments the collimator and/or sub-pixel pitch may bedifferent in different directions. Alternatively or additionally, thecollimator pitch and/or sub-pixel pitch may vary along a given direction(e.g., within a range of ratios as discussed herein). For example, asub-pixel pitch may vary along at least one of a length or width of asemiconductor detector. FIG. 5 illustrates a schematic plan view of asemiconductor detector 500 having a pixel array 501 in accordance withvarious embodiments. It may be noted that a sub-pixel pitch defined bythe pixel array 501 varies along the length 520 and the width 530 of thesemiconductor detector 500. As seen in FIG. 5, the array 501 of pixelsis defined by pixel boundaries 502 (shown in darker lines), and furthersub-divided by virtual sub-pixel boundaries 504 (shown in lighterlines). The pitch between various virtual sub-pixels (or spacing betweenadjacent sub-pixel boundaries 504) of the array 501 is different,resulting in differently sized virtual sub-pixels 510, 512, 514, 516,and 518. It may be noted that the ultimate true intrinsic spatialresolution of a detector is limited by the accuracy of the determinationof the location of the event as calculated by the sub-pixelizationalgorithm, and thus is limited by signal noise rather than the(arbitrary) selection of the sub-pixels'sizes.

FIG. 6 provides a flowchart of a method 600 for providing an imagingdetector assembly in accordance with various embodiments. The method 600(or aspects thereof), for example, may employ or be performed bystructures or aspects of various embodiments (e.g., systems and/ormethods and/or process flows) discussed herein. In various embodiments,certain steps may be omitted or added, certain steps may be combined,certain steps may be performed concurrently, certain steps may be splitinto multiple steps, certain steps may be performed in a differentorder, or certain steps or series of steps may be re-performed in aniterative fashion.

At 602, a semiconductor detector (e.g., semiconductor detector 110) isprovided. The semiconductor has a first surface and a second surfacethat are opposed to each other. The first surface includes pixelatedanodes, and the second surface comprises at least one cathode electrode.

At 604, a collimator (e.g., collimator 120) is disposed proximate thesemiconductor detector. For example, the collimator may be disposedproximate the first surface, with the collimator interposed between thefirst surface and an object to be imaged, with the collimator guidingradiation to the pixelated anodes disposed on the first surface. Thecollimator includes openings defined by septa, with each openingassociated with asingle correpsnding pixel of the semiconductordetector. The collimator defines a pitch D between adjacent sept, andthe septa define a septa length L. A ratio of L/D is less than 14 invarious embodiments. For example, in some embodiments the ratio of L/Dis less than 12. As another example, in some embodiments, the ratio ofL/D is between 8 or more and 12 or less.

At 606, a processing unit (e.g., processing unit 130) is coupled to thesemiconductor detector. The processing unit is configured to identifydetected events within virtual sub-pixels distributed along a lengthoand width of the semiconductor detector. Each pixel includes aplurality of corresponding virtual sub-pixels, with absorbed photonscounted as events in a corresponding virtual sub-pixel. The sub-pixelsdefine a pitch d. In varies embodiments, the ratio of L/d is 25 or more(e.g., between 25 or more and 80 or less).

FIG. 7 provides a flowchart of a method 700 for providing an imagingdetector assembly in accordance with various embodiments. The method 700(or aspects thereof), for example, may employ or be performed bystructures or aspects of various embodiments (e.g., systems and/ormethods and/or process flows) discussed herein. In various embodiments,certain steps may be omitted or added, certain steps may be combined,certain steps may be performed concurrently, certain steps may be splitinto multiple steps, certain steps may be performed in a differentorder, or certain steps or series of steps may be re-performed in aniterative fashion.

At 702, signals are collected from a plurality of adjacent pixels (e.g.,of a detector). Signals are collected for each event of a plurality ofevents (e.g., corresponding to emission from a patient being imaged thathas been administered a radiopharmaceutical). At 704, a virtualsub-pixel location is calculated for each event.

At 706, an image is reconstructed. In the illustrated embodiment, athree-dimensional (3D) image is generated at 708. In the depictedembodiment, the 3D image is generated based on, for each event, avirtual sub-pixel location (e.g., a location of the event in a grid ofvirtual sub-pixels), and also based on a location of a correspondingcollimator bore associated with a pixel including the correspondingvirtual sub-pixel (e.g., the collimator bore associated with the pixelin which the event's virtual sub-pixel resides).

It may be noted that in various embodiments the use of a reconstructionalgorithm utilizing sub-pixels allows the advantages provided by thevarious structures discussed herein to be beneficially realized. Forexample, FIG. 8 shows a comparison of sub-pixel position capability forvarious different arrangements. Arrangement 810 illustrates a pixelatedmodule with a 2.46 millimeter pitch and 45 millimmeter septa height.Such an arrangement provides a 5.8 degree view spread function (VSF) anda sensitivity of 190 cpm/μC_(i). Arrangement 820 utilizes a similarstructure as 810 (e.g., 2.46 millimeter pitch and 45 millimeter septaheight). However, arrangement 820 uses a sub-pixel pitch of 0.4millimeters, providing a 3.4 degree VSF. Accordingly, arrangement 820provides improved resolution with a similar sensitivity with respect toarrangement 810. Arrangement 830 utilizes a 0.4 millimeter sub-pixelpitch, and also utilizes a 26 millimeter septa height, which is shorterthan the septa height for arrangments 810 and 820. Arrangement 830provides a 5.8 degree VSF, similar to arrangement 810, but provides asensitivity of 620 cpm/μC_(i). Accordingly, arrangement 830 provides acomparable resolution to arrangement 810, but provides approximately300% more sensitivity. Arrangement 820 provides an example of improvedresolution using sub-pixel based reconstruction, and arrangement 830provides an example of improved sensitivity using sub-pixel basedreconstruction. It may be noted that alternative arrangements usingdifferent sub-pixel pitches and/or different septa height than shown maybe utilized that provide for both improved sensitivity and resolutionrelative to arrangement 810.

FIG. 10 is a schematic illustration of a NM imaging system 1000 having aplurality of imaging detector head assemblies mounted on a gantry (whichmay be mounted, for example, in rows, in an iris shape, or otherconfigurations, such as a configuration in which the movable detectorcarriers 1016 are aligned radialy toward the patient-body 1010). Inparticular, a plurality of imaging detectors 1002 are mounted to agantry 1004. Each detector 1002 may include, for example, collimatorsand detectors arranged generally similarly to the arrangements discussedin connection with FIGS. 1-6. In the illustrated embodiment, the imagingdetectors 1002 are configured as two separate detector arrays 1006 and1008 coupled to the gantry 1004 above and below a subject 1010 (e.g., apatient), as viewed in FIG. 10. The detector arrays 1006 and 1008 may becoupled directly to the gantry 1004, or may be coupled via supportmembers 1012 to the gantry 1004 to allow movement of the entire arrays1006 and/or 1008 relative to the gantry 1004 (e.g., transversetranslating movement in the left or right direction as viewed by arrow Tin FIG. 10). Additionally, each of the imaging detectors 1002 includes adetector unit 1014 (which may include collimator and/or detectorassemblies as discussed herein), at least some of which are mounted to amovable detector carrier 1016 (e.g., a support arm or actuator that maybe driven by a motor to cause movement thereof) that extends from thegantry 1004. In some embodiments, the detector carriers 1016 allowmovement of the detector units 1014 towards and away from the subject1010, such as linearly. Thus, in the illustrated embodiment the detectorarrays 1006 and 1008 are mounted in parallel above and below the subject1010 and allow linear movement of the detector units 1014 in onedirection (indicated by the arrow L), illustrated as perpendicular tothe support member 1012 (that are coupled generally horizontally on thegantry 1004). However, other configurations and orientations arepossible as described herein. It should be noted that the movabledetector carrier 1016 may be any type of support that allows movement ofthe detector units 1014 relative to the support member 1012 and/organtry 1004, which in various embodiments allows the detector units 1014to move linearly towards and away from the support member 1012.

Each of the imaging detectors 1002 in various embodiments is smallerthan a conventional whole body or general purpose imaging detector. Aconventional imaging detector may be large enough to image most or allof a width of a patient's body at one time and may have a diameter or alarger dimension of approximately 50 cm or more. In contrast, each ofthe imaging detectors 1002 may include one or more detector units 1014coupled to a respective detector carrier 1016 and having dimensions of,for example, 4 cm to 20 cm and may be formed of Cadmium Zinc Telluride(CZT) tiles or modules. For example, each of the detector units 1014 maybe 8×8 cm in size and be composed of a plurality of CZT pixelatedmodules (not shown). For example, each module may be 4×4 cm in size andhave 16×16=256 pixels. In some embodiments, each detector unit 1014includes a plurality of modules, such as an array of 1×7 modules.However, different configurations and array sizes are contemplatedincluding, for example, detector units 1014 having multiple rows ofmodules.

It should be understood that the imaging detectors 1002 may be differentsizes and/or shapes with respect to each other, such as square,rectangular, circular or other shape. An actual field of view (FOV) ofeach of the imaging detectors 1002 may be directly proportional to thesize and shape of the respective imaging detector.

The gantry 1004 may be formed with an aperture 1018 (e.g., opening orbore) therethrough as illustrated. A patient table 1020, such as apatient bed, is configured with a support mechanism (not shown) tosupport and carry the subject 1010 in one or more of a plurality ofviewing positions within the aperture 1018 and relative to the imagingdetectors 1002. Alternatively, the gantry 1004 may comprise a pluralityof gantry segments (not shown), each of which may independently move asupport member 1012 or one or more of the imaging detectors 1002.

The gantry 1004 may also be configured in other shapes, such as a “C”,“H” and “L”, for example, and may be rotatable about the subject 1010.For example, the gantry 1004 may be formed as a closed ring or circle,or as an open arc or arch which allows the subject 1010 to be easilyaccessed while imaging and facilitates loading and unloading of thesubject 1010, as well as reducing claustrophobia in some subjects 1010.

Additional imaging detectors (not shown) may be positioned to form rowsof detector arrays or an arc or ring around the subject 1010. Bypositioning multiple imaging detectors 1002 at multiple positions withrespect to the subject 1010, such as along an imaging axis (e.g., headto toe direction of the subject 1010) image data specific for a largerFOV may be acquired more quickly.

Each of the imaging detectors 1002 has a radiation detection face, whichis directed towards the subject 1010 or a region of interest within thesubject.

In various embodiments, multi-bore collimators may be constructed to beregistered with pixels of the detector units 1014, which in oneembodiment are CZT detectors. However, other materials may be used.Registered collimation may improve spatial resolution by forcing photonsgoing through one bore to be collected primarily by one pixel.Additionally, registered collimation may improve sensitivity and energyresponse of pixelated detectors as detector area near the edges of apixel or in-between two adjacent pixels may have reduced sensitivity ordecreased energy resolution or other performance degradation. Havingcollimator septa directly above the edges of pixels reduces the chanceof a photon impinging at these degraded-performance locations, withoutdecreasing the overall probability of a photon passing through thecollimator. As discussed herein, in various embodiments parallel-holeand/or pin-hole collimation may be employed.

A controller unit 1030 may control the movement and positioning of thepatient table 1020, imaging detectors 1002 (which may be configured asone or more arms), gantry 1004 and/or the collimators 1022 (that movewith the imaging detectors 1002 in various embodiments, being coupledthereto). A range of motion before or during an acquisition, or betweendifferent image acquisitions, is set to maintain the actual FOV of eachof the imaging detectors 1002 directed, for example, towards or “aimedat” a particular area or region of the subject 1010 or along the entiresubject 1010. The motion may be a combined or complex motion in multipledirections simultaneously, concurrently, or sequentially as described inmore detail herein.

The controller unit 1030 may have a gantry motor controller 1032, tablecontroller 1034, detector controller 1036, pivot controller 1038, andcollimator controller 1040. The controllers 1030, 1032, 1034, 1036,1038, 1040 may be automatically commanded by a processing unit 1050,manually controlled by an operator, or a combination thereof. The gantrymotor controller 1032 may move the imaging detectors 1002 with respectto the subject 1010, for example, individually, in segments or subsets,or simultaneously in a fixed relationship to one another. For example,in some embodiments, the gantry controller 1032 may cause the imagingdetectors 1002 and/or support members 1012 to move relative to or rotateabout the subject 1010, which may include motion of less than or up to180 degrees (or more).

The table controller 1034 may move the patient table 1020 to positionthe subject 1010 relative to the imaging detectors 1002. The patienttable 1020 may be moved in up-down directions, in-out directions, andright-left directions, for example. The detector controller 1036 maycontrol movement of each of the imaging detectors 1002 to move togetheras a group or individually as described in more detail herein. Thedetector controller 1036 also may control movement of the imagingdetectors 1002 in some embodiments to move closer to and farther from asurface of the subject 1010, such as by controlling translating movementof the detector carriers 1016 linearly towards or away from the subject1010 (e.g., sliding or telescoping movement). Optionally, the detectorcontroller 1036 may control movement of the detector carriers 1016 toallow movement of the detector array 1006 or 1008. For example, thedetector controller 1036 may control lateral movement of the detectorcarriers 1016 illustrated by the T arrow (and shown as left and right asviewed in FIG. 10). In various embodiments, the detector controller 1036may control the detector carriers 1016 or the support members 1012 tomove in different lateral directions. Detector controller 1036 maycontrol the swiveling motion of detectors 1002 together with theircollimators 1022.

The pivot controller 1038 may control pivoting or rotating movement ofthe detector units 1014 at ends of the detector carriers 1016 and/orpivoting or rotating movement of the detector carrier 1016. For example,one or more of the detector units 1014 or detector carriers 1016 may berotated about at least one axis to view the subject 1010 from aplurality of angular orientations to acquire, for example, 3D image datain a 3D SPECT or 3D imaging mode of operation. The collimator controller1040 may adjust a position of an adjustable collimator, such as acollimator with adjustable strips (or vanes) or adjustable pinhole(s).

It should be noted that motion of one or more imaging detectors 1002 maybe in directions other than strictly axially or radially, and motions inseveral motion directions may be used in various embodiment. Therefore,the term “motion controller” may be used to indicate a collective namefor all motion controllers. It should be noted that the variouscontrollers may be combined, for example, the detector controller 1036and pivot controller 1038 may be combined to provide the differentmovements described herein.

Prior to acquiring an image of the subject 1010 or a portion of thesubject 1010, the imaging detectors 1002, gantry 1004, patient table1020 and/or collimators 1022 may be adjusted, such as to first orinitial imaging positions, as well as subsequent imaging positions. Theimaging detectors 1002 may each be positioned to image a portion of thesubject 1010. Alternatively, for example in a case of a small sizesubject 1010, one or more of the imaging detectors 1002 may not be usedto acquire data, such as the imaging detectors 1002 at ends of thedetector arrays 1006 and 1008, which as illustrated in FIG. 10 are in aretracted position away from the subject 1010. Positioning may beaccomplished manually by the operator and/or automatically, which mayinclude using, for example, image information such as other imagesacquired before the current acquisition, such as by another imagingmodality such as X-ray Computed Tomography (CT), MRI, X-Ray, PET orultrasound. In some embodiments, the additional information forpositioning, such as the other images, may be acquired by the samesystem, such as in a hybrid system (e.g., a SPECT/CT system).Additionally, the detector units 1014 may be configured to acquirenon-NM data, such as x-ray CT data. In some embodiments, amulti-modality imaging system may be provided, for example, to allowperforming NM or SPECT imaging, as well as x-ray CT imaging, which mayinclude a dual-modality or gantry design as described in more detailherein.

After the imaging detectors 1002, gantry 1004, patient table 1020,and/or collimators 1022 are positioned, one or more images, such asthree-dimensional (3D) SPECT images are acquired using one or more ofthe imaging detectors 1002, which may include using a combined motionthat reduces or minimizes spacing between detector units 1014. The imagedata acquired by each imaging detector 1002 may be combined andreconstructed into a composite image or 3D images in variousembodiments.

In one embodiment, at least one of detector arrays 1006 and/or 1008,gantry 1004, patient table 1020, and/or collimators 1022 are moved afterbeing initially positioned, which includes individual movement of one ormore of the detector units 1014 (e.g., combined lateral and pivotingmovement) together with the swiveling motion of detectors 1002. Forexample, at least one of detector arrays 1006 and/or 1008 may be movedlaterally while pivoted. Thus, in various embodiments, a plurality ofsmall sized detectors, such as the detector units 1014 may be used for3D imaging, such as when moving or sweeping the detector units 1014 incombination with other movements.

In various embodiments, a data acquisition system (DAS) 1060 receiveselectrical signal data produced by the imaging detectors 1002 andconverts this data into digital signals for subsequent processing.However, in various embodiments, digital signals are generated by theimaging detectors 1002. An image reconstruction device 1062 (which maybe a processing device or computer) and a data storage device 1064 maybe provided in addition to the processing unit 1050. It should be notedthat one or more functions related to one or more of data acquisition,motion control, data processing and image reconstruction may beaccomplished through hardware, software and/or by shared processingresources, which may be located within or near the imaging system 1000,or may be located remotely. Additionally, a user input device 1066 maybe provided to receive user inputs (e.g., control commands), as well asa display 1068 for displaying images. DAS 1060 receives the acquiredimages from detectors 1002 together with the corresponding lateral,vertical, rotational and swiveling coordinates of gantry 1004, supportmembers 1012, detector units 1014, detector carriers 1016, and detectors1002 for accurate reconstruction of an image including 3D images andtheir slices.

It may be noted that the embodiment of FIG. 10 may be understood as alinear arrangement of detector heads (e.g., utilizing detector unitsarranged in a row and extending parallel to one another. In otherembodiments, a radial design may be employed. Radial designs, forexample, may provide additional advantages in terms of efficientlyimaging smaller objects, such as limbs, heads, or infants. FIG. 11provides a schematic view of a nuclear medicine (NM) multi-head imagingsystem 1100 in accordance with various embodiments. Generally, theimaging system 1100 is configured to acquire imaging information (e.g.,photon counts) from an object to be imaged (e.g., a human patient) thathas been administered a radiopharmaceutical. The depicted imaging system1100 includes a gantry 1110 having a bore 1112 therethrough, pluralradiation detector head assemblies 1115, and a processing unit 1120.

The gantry 1110 defines the bore 1112. The bore 1112 is configured toaccept an object to be imaged (e.g., a human patient or portionthereof). As seen in FIG. 11, plural radiation detector head assemblies1115 are mounted to the gantry 1110. In the illustrated embodiment, eachradiation detector head assembly 1115 includes an arm 1114 and a head1116. The arm 1114 is configured to articulate the head 1116 radiallytoward and/or away from a center of the bore 1112 (and/or in otherdirections), and the head 1116 includes at least one detector, with thehead 1116 disposed at a radially inward end of the arm 1114 andconfigured to pivot to provide a range of positions from which imaginginformation is acquired.

The detector of the head 1116, for example, may be a semiconductordetector. For example, a semiconductor detector various embodiments maybe constructed using different materials, such as semiconductormaterials, including Cadmium Zinc Telluride (CdZnTe), often referred toas CZT, Cadmium Telluride (CdTe), and Silicon (Si), among others. Thedetector may be configured for use with, for example, nuclear medicine(NM) imaging systems, positron emission tomography (PET) imagingsystems, and/or single photon emission computed tomography (SPECT)imaging systems.

In various embodiments, the detector may include an array of pixelatedanodes, and may generate different signals depending on the location ofwhere a photon is absorbed in the volume of the detector under a surfaceif the detector. The volumes of the detector under the pixelated anodesare defined as voxels (not shown in FIG. 1). For each pixelated anode,the detector has a corresponding voxel. The absorption of photons bycertain voxels corresponding to particular pixelated anodes results incharges generated that may be counted. The counts may be correlated toparticular locations and used to reconstruct an image.

In various embodiments, each detector head assembly 1115 may define acorresponding view that is oriented toward the center of the bore 1112.Each detector head assembly 1115 in the illustrated embodiment isconfigured to acquire imaging information over a sweep rangecorresponding to the view of the given detector unit. Additional detailsregarding examples of systems with detector units disposed radiallyaround a bore may be found in U.S. patent application Ser. No.14/788,180, filed 30 Jun. 2015, entitled “Systems and Methods ForDynamic Scanning With Multi-Head Camera,” the subject matter of which isincorporated by reference in its entirety.

The processing unit 1120 includes memory 1122. The imaging system 1100is shown as including a single processing unit 1120; however, the blockfor the processing unit 1120 may be understood as representing one ormore processors that may be distributed or remote from each other. Thedepicted processing unit 1120 includes processing circuitry configuredto perform one or more tasks, functions, or steps discussed herein. Itmay be noted that “processing unit” as used herein is not intended tonecessarily be limited to a single processor or computer. For example,the processing unit 1120 may include multiple processors and/orcomputers, which may be integrated in a common housing or unit, or whichmay distributed among various units or housings.

Generally, various aspects (e.g., programmed modules) of the processingunit 1120 act individually or cooperatively with other aspects toperform one or more aspects of the methods, steps, or processesdiscussed herein. In the depicted embodiment, the memory 1122 includes atangible, non-transitory computer readable medium having stored thereoninstructions for performing one or more aspects of the methods, steps,or processes discussed herein.

By, for example, utilizing shorter septa heights, various embodimentsprovide for more compact detector head sizes. Use of smaller detectorhead sizes can provide improved imaging (e.g., decreased tail, improvedresolution, and/or improved sensitivity) while also allowing for closerplacement to smaller objects to be imaged. For example, FIG. 12 shows afirst system 1210 having detector units 1212 that have a septa height of18 millimeters and a detector unit diameter of 77 millimeters. As seenin FIG. 12, the detector units 1212 of first system 1210 may be extendedto an inward position defining a radius of 129 millimeters. Secondsystem 1220 has detector units 1222 that have a septa height of 15millimeters and a detector unit diameter of 74 millimeters. As seen inFIG. 12, the detector units 1222 of second system 1220 may be extendedto an inward position defining a radius of 124 millimeters, allowing forcloser placement to smaller objects than is possible for first system1210.

It should be noted that the various embodiments may be implemented inhardware, software or a combination thereof. The various embodimentsand/or components, for example, the modules, or components andcontrollers therein, also may be implemented as part of one or morecomputers or processors. The computer or processor may include acomputing device, an input device, a display unit and an interface, forexample, for accessing the Internet. The computer or processor mayinclude a microprocessor. The microprocessor may be connected to acommunication bus. The computer or processor may also include a memory.The memory may include Random Access Memory (RAM) and Read Only Memory(ROM). The computer or processor further may include a storage device,which may be a hard disk drive or a removable storage drive such as asolid-state drive, optical disk drive, and the like. The storage devicemay also be other similar means for loading computer programs or otherinstructions into the computer or processor.

As used herein, the term “computer” or “module” may include anyprocessor-based or microprocessor-based system including systems usingmicrocontrollers, reduced instruction set computers (RISC), ASICs, logiccircuits, and any other circuit or processor capable of executing thefunctions described herein. The above examples are exemplary only, andare thus not intended to limit in any way the definition and/or meaningof the term “computer”.

The computer or processor executes a set of instructions that are storedin one or more storage elements, in order to process input data. Thestorage elements may also store data or other information as desired orneeded. The storage element may be in the form of an information sourceor a physical memory element within a processing machine.

The set of instructions may include various commands that instruct thecomputer or processor as a processing machine to perform specificoperations such as the methods and processes of the various embodiments.The set of instructions may be in the form of a software program. Thesoftware may be in various forms such as system software or applicationsoftware and which may be embodied as a tangible and non-transitorycomputer readable medium. Further, the software may be in the form of acollection of separate programs or modules, a program module within alarger program or a portion of a program module. The software also mayinclude modular programming in the form of object-oriented programming.The processing of input data by the processing machine may be inresponse to operator commands, or in response to results of previousprocessing, or in response to a request made by another processingmachine.

As used herein, a structure, limitation, or element that is “configuredto” perform a task or operation is particularly structurally formed,constructed, or adapted in a manner corresponding to the task oroperation. For purposes of clarity and the avoidance of doubt, an objectthat is merely capable of being modified to perform the task oroperation is not “configured to” perform the task or operation as usedherein. Instead, the use of “configured to” as used herein denotesstructural adaptations or characteristics, and denotes structuralrequirements of any structure, limitation, or element that is describedas being “configured to” perform the task or operation. For example, aprocessing unit, processor, or computer that is “configured to” performa task or operation may be understood as being particularly structuredto perform the task or operation (e.g., having one or more programs orinstructions stored thereon or used in conjunction therewith tailored orintended to perform the task or operation, and/or having an arrangementof processing circuitry tailored or intended to perform the task oroperation). For the purposes of clarity and the avoidance of doubt, ageneral purpose computer (which may become “configured to” perform thetask or operation if appropriately programmed) is not “configured to”perform a task or operation unless or until specifically programmed orstructurally modified to perform the task or operation.

As used herein, the terms “software” and “firmware” are interchangeable,and include any computer program stored in memory for execution by acomputer, including RAM memory, ROM memory, EPROM memory, EEPROM memory,and non-volatile RAM (NVRAM) memory. The above memory types areexemplary only, and are thus not limiting as to the types of memoryusable for storage of a computer program.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the variousembodiments without departing from their scope. While the dimensions andtypes of materials described herein are intended to define theparameters of the various embodiments, they are by no means limiting andare merely exemplary. Many other embodiments will be apparent to thoseof skill in the art upon reviewing the above description. The scope ofthe various embodiments should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects. Further, the limitations of the followingclaims are not written in means-plus-function format and are notintended to be interpreted based on 35 U.S.C. §112(f) unless and untilsuch claim limitations expressly use the phrase “means for” followed bya statement of function void of further structure.

This written description uses examples to disclose the variousembodiments, including the best mode, and also to enable any personskilled in the art to practice the various embodiments, including makingand using any devices or systems and performing any incorporatedmethods. The patentable scope of the various embodiments is defined bythe claims, and may include other examples that occur to those skilledin the art. Such other examples are intended to be within the scope ofthe claims if the examples have structural elements that do not differfrom the literal language of the claims, or the examples includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

What is claimed is:
 1. A nuclear medicine imaging system comprising: agantry including a bore; and a plurality of detector head assembliesmounted to the gantry, wherein each of the plurality of detector headassemblies comprises: a head attached to an arm, wherein the arm isconfigured to articulate the head both radially toward a center of thebore and radially away from the center of the bore, wherein the headcomprises at least one detector unit disposed at a radially inward endof the arm, and wherein the head is configured to pivot with respect tothe arm; wherein the at least one detector unit comprises: asemiconductor detector including a first surface and a second surfaceopposed to the first surface, wherein the first surface comprisespixelated anodes and the second surface comprises a cathode electrode;and a collimator including openings defined by septa, the collimatordefining a pitch D between adjacent septa, the septa defining a septalength L, wherein a ratio of L/D is less than 14; wherein each of theplurality of detector head assemblies may be extended to an inwardposition defining a radius of 129 millimeters or less.
 2. The nuclearmedicine imaging system of claim 1, wherein each of the plurality ofdetector head assemblies may be extended to an inward position defininga radius of less than 129 millimeters.
 3. The nuclear medicine imagingsystem of claim 1, wherein each of the plurality of detector headassemblies may be extended to an inward position defining a radius of129 millimeters.
 4. The nuclear medicine imaging system of claim 1,wherein each of the plurality of detector head assemblies may beextended to an inward position defining a radius of 124 millimeters orless.
 5. The nuclear medicine imaging system of claim 1, wherein each ofthe plurality of detector head assemblies may be extended to an inwardposition defining a radius of 124 millimeters.
 6. The nuclear medicineimaging system of claim 1, wherein the plurality of detector headassemblies comprises at least five detector head assemblies.
 7. Thenuclear medicine imaging system of claim 1, wherein the plurality ofdetector head assemblies comprises twelve detector head assemblies.
 8. Anuclear medicine imaging system comprising: a gantry including a bore;and a plurality of detector head assemblies mounted to the gantry,wherein each of the plurality of detector head assemblies comprises: ahead attached to an arm, wherein the arm is configured to articulate thehead both radially toward a center of the bore and radially away fromthe center of the bore, wherein the head comprises at least one detectorunit disposed at a radially inward end of the arm, and wherein the headis configured to pivot with respect to the arm; wherein the at least onedetector unit comprises: a semiconductor detector including a firstsurface and a second surface opposed to the first surface, wherein thefirst surface comprises pixelated anodes and the second surfacecomprises a cathode electrode; and a collimator including openingsdefined by septa; wherein the detector unit has an outer diameter of 77millimeters or less; wherein each of the plurality of detector headassemblies may be extended to an inward position defining a radius of129 millimeters or less.
 9. The nuclear medicine imaging system of claim8, wherein the plurality of detector head assemblies comprises at leastfive detector head assemblies.
 10. The nuclear medicine imaging systemof claim 9, wherein the detector unit has an outer diameter of 77millimeters.
 11. The nuclear medicine imaging system of claim 9, whereinthe detector unit has an outer diameter of 74 millimeters or less.
 12. Anuclear medicine imaging system comprising: a gantry including a bore;and a plurality of detector head assemblies mounted to the gantry,wherein each of the plurality of detector head assemblies comprises: ahead attached to an arm, wherein the arm is configured to articulate thehead both radially toward a center of the bore and radially away fromthe center of the bore, wherein the head comprises at least one detectorunit disposed at a radially inward end of the arm, and wherein the headis configured to pivot with respect to the arm; wherein the at least onedetector unit comprises: a semiconductor detector including a firstsurface and a second surface opposed to the first surface, wherein thefirst surface comprises pixelated anodes and the second surfacecomprises a cathode electrode; and a collimator including openingsdefined by septa having a septa height of 18 millimeters or less;wherein each of the plurality of detector head assemblies may beextended to an inward position defining a radius of 129 millimeters orless.
 13. The nuclear medicine imaging system of claim 12, wherein thesepta height is 18 millimeters.
 14. The nuclear medicine imaging systemof claim 12, wherein the septa height is 15 millimeters or less.
 15. Thenuclear medicine imaging system of claim 14, wherein the septa height is15 millimeters.
 16. The nuclear medicine imaging system of claim 12,wherein the detector unit has an outer diameter of 77 millimeters orless.
 17. The nuclear medicine imaging system of claim 12, wherein thedetector unit has an outer diameter of 74 millimeters or less.
 18. Thenuclear medicine imaging system of claim 14, wherein the detector unithas an outer diameter of 77 millimeters or less.
 19. The nuclearmedicine imaging system of claim 14, wherein the detector unit has anouter diameter of 74 millimeters or less.
 20. The nuclear medicineimaging system of claim 12, wherein wherein the plurality of detectorhead assemblies comprises at least five detector head assemblies.